Optical control device

ABSTRACT

An optical control device responsive to a localized source of light by means of a quadrant array detector means being mounted on an electromagnetic flexure means for controlling the position of said detector means relative to said localized source of light so as to proportion said source of localized light equally in each of said detector quadrants. The device further has electronic closed-loop means responsive to said quadrant array detector means intermediate said quadrant array detector means and said electromagnetic flexure means.

I United States Patent ml 3,591,292

[72] Inventors Wilfred C. Feuchter [55] Rcferenggs Cit d r 'z tfl -l MMk I d UNITED STATES PATENTS t 3,260,849 7/l966 Poyle. 250 203 Clement P.Means, Ann Arbor, Mtcln,

$263,088 7/1966 Goldfischer 356/[41 Mll'Vlll Weks, Ann Arbor, Mich.,Jerome 3,290,505 12/1966 Stavis 250/203FiroendeoeueddateotsoutliBentLlntL, 3470 377 91969 L F b 0 2 3 Burton L.Lockwood, admin'strator, I e C re 25 l O Mishawalia, lud. PrimaryExaminer-Rodney D. Bennett, Jr. (21 Appl. No. 740,424 AssistantExaminerloseph G4 Baxter [22] Filed June 3, I968 ArtorneysC. F, Arensand Flame, Arens, Hartz & O'Brien [45] Patented July 6, I971 [73]Assignee The Bendix Corporation ABSTRACT: An optical control deviceresponsive to a localized source of light by means of a quadrant arraydetector means being mounted on an electromagnetic flexure means (54] sgF P for controlling the position of said detector means relative to saidlocalized source of li ht so as to pro ortion said source of g P [52]US. Cl. 356/l4l, localized light equally in each of said detectorquadrants. The 250/203 device further has electronic closed-loop meansresponsive to [5]] Int. 11/26 said quadrant array detector meansintermediate said [50] Field of Search 356/141; quadrant array detectormeans and said electromagnetic flex- 250/203 ure means 8 20 Mice OPTICSr M A A ET. B A58.

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INT.

TARGET ACQUISITION MODE PATENIEUJUL smn SHEET 2 [IF 3 OPTICAL CONTROLDEVICE BACKGROUND OF THE INVENTION The invention relates to opticalcontrol devices of the variety generally used in association with targettracking or weapon guidance applications. However, it is felt that theinvention is sufficiently broad in concept to facilitate its use for anyapplication where optical control is required.

The conventional optical control devices with which we are familiar arecomprised of closed-loop tracking systems that employ gears, motors,pivots, linkages or other similar mechanical mechanisms to acquire andretain detection of the target image by the photosensitive element.These concepts require numerous moving parts, and thus, are costly tomanufacture and maintain. Moreover, these unduly complex systems haveproven themselves to be unreliable, resulting in loss of targettracking.

SUMMARY OF THE INVENTION It is the purpose of this invention to providean optical control device that employs a quadrant array photodetectorwhich facilitates the use of amplitude monopulse electronic signalprocessing, and to mount the photodetector on a twoaxis electromagneticflexure means which reduces the number of moving parts to one. Aclosed-loop electronic array photodetector electrically produces twomagnetic fields which result in two forces, one each to deflect thevertical and horizontal components of the flexure means. Further, theuse of the amplitude monopulse signal-processing technique incombination with an optical control device of the type described hereinallows this system to operate with continuous or intermittent lightsources, and with regular or random pulse repetition rates.Additionally, the simplicity of this system will result in a substantialcost reduction over prior devices as well as perform very reliably inits use environment.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof embodiments of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of theoptical control device;

FIG. 2 is a front view of the quadrant array photodetector depicting anon-axis image;

FIG. 3 is a front view of the quadrant array photodetector depicting animage having its vertical and horizontal components off center;

FIG. 4 is a pictorial perspective, partly sectioned, view of a trackingsystem embodying this invention;

FIG. 5 is a perspective view of the detector assembly depicting itsfunctional elements;

FIG. 6 is a pictorial perspective, partly sectioned, view of a missileguidance system depicting a modified form of this invention; and

FIG. 7 is a view of FIG. 6 looking from the front.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings andparticularly to FIG. 1, the optical control device is indicated byreference numeral Ill. The optical control device 10 is pictoriallyshown in FIG 4 cmbodied in a tracking system application. Further, itsfunctional capabilities are such that it can be adapted for a variety oftracking applications.

The optical control device 10 is responsive to a localized source oflight 12. Said localized source of light approaches that of a pointsource and has a wavelength of emission that lies in the visible or nearinfrared portions of the electromagnetic spectrum. In a trackingapplication, the optical control device 10 may be used for tracking alocalized light source 12, such as an injection laser mounted on aguided missile.

Detector assembly 14 of optical control device 10 is comprised of atwo-axis electromagnetic flexure means 16 and a quadrant array detectormeans 18 and is responsive to said localized source of light 12 throughan optical means 20 and a filter means 22.

The filter means 22 is employed to limit the spectral response of saidquadrant array detector 18 and thereby improve the signal-to-noise ratioof the optical tracking device I0. As can be seen by those skilled inthe art, the spectrum to which filter means 22 is responsive may beoptimized to cooperate with said quadrant array detector 18 for avariety of tracking requirements.

The optical system 20 uses conventional lens and image collection forproviding light inputs to said quadrant array detector 18. The specificdesign parameters associated with the optical system 20 and the field ofview of the optical tracking device It) may be readily determined byanyone skilled in the art and adapted to suit whatever specific trackingrequirement that may exist.

The array detector means 18, as shown best in FIG. 2, is comprised ofphotodiodes 24, 26, 28, and 30, forming the quadrants of a circle andbeing fixed to mounting plate 32. The spacing between said diodes isvery close to maximize the photosensitive inner area of the arraydetector means I8. These solid-state detector diodes may be optimized interms of sensitivity and speed for any particular spectral region ofinterest. In response to a source of light I2 the photodiodes 24, 26,28, and 30, will provide output signals A, B, C, and D, respectively.For a pulsed source of light I2, the photodiode output signals A, B, C,and D, are pulses whose amplitude is proportional to the incident energyfalling on each of the diodes. If the object point 34 from the source oflight 12 is onaxis, as shown in FIG. 2, the four pulses are equal inamplitude', i.e., A=B=C=D. If an object point 36 from the source oflight12 is ofi-axis, as shown in FIG. 3, the four pulses would be unequal inamplitude. The sensing principle of the tracking system 10 results fromthe fact that when an image from the light source 12 falls slightlyoff-axis of the detector means 18, an unbalance will exist in outputsignals A, B, C, and D, from the photodetector quadrants. These outputsmay then be expressed as error signals in terms of vertical andhorizontal displacement from an on-axis balanced condition. Thus, anyunbalanced condition will have a vertical and/or horizontal signal errorto reestablish the on-axis balanced condition.

The vertical signal error or pitch angular error, 9p, is a knownfunction of Y.

Y As-l-B(C+D) A, B, C, and D are the amplitudes of the four pulses.

The horizontal signal error or yaw angular error, 0y, is a knownfunction of X.

Therefore, vertical and horizontal error signals are available from thephotodiode outputs A, B, C, and D, relating their position relative tosaid source of light 12.

Referring now to FIGS. 4 and 5, the two axis electromag netic flexuremeans I6 is comprised of a cantilevered means 40 rigidly attached to aflexible member or shaft 41 which, in turn, is rigidly fastened to amounting means 42 for suitably mounting to the structure of said opticaltracking device 10 on surface 43, a first torquer coil 44 having aninput 46 and output 47 for controlling vertical axis position, a secondtorquer coil 48 (represented by a broken line) having an input 50 andoutput 52 for controlling horizontal axis position, a first pickoff coil54 having an input 56 and an output 58 and being magnetically responsiveto said torquer coil 44 to provide a vertical feedback signal, a secondpickoff coil 60 (represented by a broken line) having an input 62 and anoutput 64 being magnetically responsive to said torquer coil 49 toprovide a horizontal feedback signal, and a mounting surface 66 at itsfree end. the two-axis electromagnetic flexure means I6 has saidquadrant array detector means I8 rigidly mounted on surface 66 toprovide a means of physically moving the detector means 18 as a functionof electronic closed-loop error-measuring circuitry responsive to saiddetector means vertical and horizontal error signals.

The optical tracking device further has a magnifying scope means 68rigidly attached thereto for accomplishing tracking system targetlock-on through visual observance by the tracking system operator.Therefore, during target acquisition mode the two-axis electromagneticflexure means 16 is boresighted with the scope means 68 to insure thatsaid quadrant array detector 18 sees the identical target that theoperator sees at the instant the operator switches from targetacquisition mode to target track mode by means of switch 70, shown inFIG. 1.

At the instant the optical tracking device 10 is switched to thetarget-tracking mode, said device functions as a closed loop system. Asumming circuit 72 is responsive to said quadrant array detector outputsA, B, C, and D, to derive a reference signal A+B+C+D. A subtractorcircuit 74 is responsive to said quadrant array detector outputs A and Dto derive an error signal A-D. A subtractor circuit 76 is responsive tosaid quadrant array detector outputs B and C to derive an error signal8-6. A summing circuit 78 is responsive to subtractor circuit 74 and 76outputs to derive a vertical position error signal A+B(C+D). Asubtracting circuit 80 is responsive to subtractor circuit 74 and 76outputs to derive a horizontal position error signal A+C(B+D). The aboveaddition and subtraction of signals A, B, C, and D from the quadrantarray detector means 18 may be accomplished with conventional pulsetransformers without degrading the signalto-noise ratio of the system.Further, if the summing and differencing is done by pulse transformers,it will be relatively easy to optimize the match of detector outputimpedance to the input impedance of the following circuitry.Additionally, it is noted that the error signals may have plus or minussignal voltage level.

A first amplifier 82 is responsive to reference signal A+B+C +0 toprovide a predetermined amount of gain thereto. Said amplifier 82further has a predetermined bandwidth which presets overall systemresponse. To detect the presence of a localized source of light in pulseform. said reference signal A+B+azD is passed through a'thresholddetector 84. The threshold voltage of said threshold detector 84 isadjusted at the minimum signal level to optimize the ratio of targetdetection probability to false target detection probability. When saidsignal A+B+C+D exceeds the threshold voltage setting a trigger pulse issupplied to a gate generator 86. Said gate generator 86 has a pulseoutput for controlling the flow of signals A+B+C+D, A+B(C+D) andA+C(B+D) through the system. Reference signal A+B+C+D is passed from theoutput of said amplifier 82 through a time delay network 88 to a gate 90to obtain coincidence between said signal A+B+C +0 and said gategenerator 86 pulse output. Said gate 90 is opened in response to saidgate generator pulse output to pass reference signal A-t-B-i-C-t-D to asample and hold circuit 92. A sample pulse generator 94 is responsive tothe trailing edge of said gate generator 86 pulse output to generate anoutput pulse. Said sample and hold circuit 92 accepts signal A+B+C +Dflow from gate 90 during the time interval said gate generator 86 has apulse output and provides an output pulse to an amplifier and filternetwork 96 in response to said sample pulse generator 94 output pulse.The amplifier and filter network 96 provides automatic gain control andclosed-loop stability feedback to said first amplifier 82. Said gate 90is comprised of a field effect transistor which provides bipolar atingaction, an RC filter, and an emitter follower stage, in that signal floworder. The action of the filter is to provide some degree of pulseaveraging while the gate 90 is open and to give several microseconds ofpulse stretching after the gate 90 is closed. The emitter follower stageis used to drive the sample and hold circuit 92 which is comprised ofafield efi'ect transistor and a storage capacitor. Said sample pulsegenerator 94 has an output pulse of about l-microsecond duration.

A second amplifier 98 is responsive to said horizontal position errorsignal A-i-C(B+D) to provide a predetermined amount of gain thereto. Thesignal A+C(B+D) is passed from the output of said amplifier 98 through atime delay network 100 to gate 102 to obtain coincidence between saidsignal A+C(B+D) and said gate generator 86 pulse output. Said gate 102is opened in response to said gate generator pulse output to passhorizontal position error signal A-i-C- 3+0 to a sample and hold circuit104. Said sample and hold circuit 104 accepts signal A+C(B+D) flow fromgate 102 during the time interval said gate generator 86 has a pulseoutput, and provides an output pulse to an integrator circuit 106. Saidgate 102 is comprised of a field effect transistor which providesbipolar gating action, an RC filter, and an emitter follower stage, inthat signal flow order. The action of the filter is to provide somedegree of pulse averaging while the gate 102 is open and to give severalmicroseconds of pulse stretching after the gate 102 is closed. Theemitter follower stage is used to drive the sample and hold circuit 104which is comprised of a field effect transistor and a storage capacitor.Thus, the pulse stretching puts more energy into the storage capacitorthan would the error pulse without stretching, which results in a pulsepower gain input to said integrator circuit 106. The integrator circuit106 is a high-gain servoamplifier whose output current is proportionalto said horizontal position error signal A+CB+D) input. The overallhorizontal tracking loop is closed through the two-axis electromagneticflexure means 16 of detector assembly 14 which receives the outputcurrent of integrator circuit 106 through switch 70. Said integratorcircuit 106 output current is passed through said torquer coil 48 toelectromagnetically move said two-axis electromagnetic flexure means 16to horizontally align said quadrant array detector l8 symmetrically withrespect to said source of localized light 12. This horizontal movementmay be in either direction. The pickoff coil 60, being magneticallyresponsive to said torquer coil 48, therefore has a current developedtherein proportional to the current in torquer coil 48. This pickoffcoil current is used as feedback from the detector assembly 14 to theinput of said integrator circuit 106 to provide said integrator circuit106 a stable closed-loop relative to said two-axis electromagneticflexure means 16. Horizontal move ment of said flexure means 16 willcontinue until the error signal input A+C--(B+D) to said integratorcircuit 106 is nulled as a result of said array detector beinghorizontally centered relative to said localized source oflight 12.

A third amplifier 108 is responsive to said vertical position errorsignal A+B(C+D) to provide a predetermined amount of gain thereto. Thesignal A+B-(C+D) is passed from the output of said amplifier 108 througha time delay network 1 10 to a gate 112 to obtain coincidence betweensaid signal A+B (C+D) and said gate generator 86 pulse output. Said gate112 is opened in response to said gate generator pulse output to passvertical position error signal A+B(C+D) to a sample and hold circuit114. Said sample and hold circuit 114 accepts signal A+B-(C+D) flow fromgage 112 during the time interval said gate generator 86 has a pulseoutput, and provides an output pulse to an integrator circuit 116. Saidgate 112 is comprised of a field effect transistor which providesbipolar gating action, an RC filter, and an emitter follower stage, inthat signal flow order. The action of the filter is to provide somedegree of pulse averaging while the gate 112 is open and to give severalmicroseconds of pulse stretching after the gate 112 is closed. Theemitter follower stage is used to drive the sample and hold circuit 114which is comprised of a field effect transistor and a storage capacitor.Thus, the pulse stretching puts more energy into the storage capacitorthan would the error pulse without stretching, which results in a pulsepower gain input to said integrator circuit 116. The integrator circuit116 is a high-gain servoamplifier whose output current is proportionalto said vertical position error signal A-i-B-C+D) input. The overallvertical tracking loop is closed through the two-axis electromagneticflexure means 16 of detector assembly 14 which receives the outputcurrent of integrator circuit "6 through switch 70. Said integratorcircuit I16 output current is passed through said torquer coil 44 toelectromagnetically move said two-axis electromagnetic flexure means 16to vertically align said quadrant array detector 18 symmetrically withrespect to said source of localized light [2. This vertical movement maybe in either direction. The pickoff coil 54, being magneticallyresponsive to said torquer coil 44, therefore has a current developedtherein proportional to the current in torquer coil 44. This pickoffcoil current is used as feedback from the detector assembly 14 to theinput of said integrator circuit 116 to provide said integrator circuit116 a stable closed-loop relative to said two-axis elec tromagneticflexure means 16. Vertical movement of said flexure means 16 willcontinue until the error signal input A+B (C+D) to said integratorcircuit 1 I6 is nulled as a result of said array detector beingvertically centered relative to said localized source oflight 12.

The required power supplies for the electronics may be supplied by anyone of the conventional techniques since stringent controls on currents,voltages and total power are not imposed by the optical control device10.

Additionally, meters 120 and I22 are responsive, respectively, todisplay vertical and horizontal angular error between the opticaltracking device boresight and the radiant source of localized light 12.

MODE OF OPERATION OF THE PREFERRED EMBODIMENT To properly accomplishtarget acquisition, the optical tracking device 10 must be suitablymounted for tracking an airborne guided missile or similar object havingmounted thereon a localized source of light, such as an injection laser.Moreover, the switch 70 must be positioned in the target acquisitionmode.

The operator of the optical tracking device will, where possible,visually acquire the target he desires to track. The operator will thenmaneuver the optical tracking device 10 until the vertical andhorizontal crosshairs of the sighting scope 68 are directly centered onthe target. The operator will then throw switch 70 to the targettracking mode position.

During the period of time required for target acquisition, while in thetarget acquisition mode, the outputs of said integrator circuits I06 and116 will be respectively, shorted to their inputs by means of switch 70to preclude their output error signals from deflecting the detectorassembly 14 and disturbing the boresighting between said detectorassembly 14 and said sighting scope 68.

When switch 70 is placed in the target tracking mode position saidintegrator circuits 106 and 116 will be connected to their respectivetorquer coils 48 and 44 and the optical tracking device will operate asa closed-loop system. it is assumed that upon initiation of targettracking the target source of light is centered vertically andhorizontally with respect to said quadrant array detector means 18.Thus, vertical or horizontal error signals will not be developed tocause deflection of said two axis electromagnetic flexure means 16 and anulled condition will exist. However, since the target may be moving ata high velocity its vertical and horizontal position relative to thenulled condition may change rapidly. It is assumed now, that the targethas moved from the on-axis or nulled condition, depicted in FIG. 2, to adifferent vertical and horizontal position as shown in FIG. 3. Since themagnitude of the outputs from each quadrant of the array detector 18 isa function of the quadrant area exposed to the source of light, therelationship of the outputs of the quadrants is as follows: B A DC. Itis assumed further, that the target is of sufficient intensity to berecognized by said threshold detector circuit 84 as a real target, whichallows the system to be responsive to vertical and horizontal errorsignals. The summing circuit 78 will derive a vertical position errorsignal A+B(C+D) which will pass through amplifier 108, time delay ll0,gate 112, sample and hold circuit 114 and into integrator circuit I16 todevelop current through torquer coil 44 and thus deflect the flexuremeans 16 up in a vertical direction until signals A+B =C+D. Thiscondition will again establish a vertical null. The subtracting circuitwill derive a horizontal position error signal A+C(B+D) which will passthrough amplifier 98, time delay I00, gate 102, sample and hold circuit104 and into integrator circuit 106 to develop current through torquercoil 48 and thus deflect the flexure means 16 to the right (as viewedfrom the quadrant array detector 18 end of the flexure means 16) untilsignals A+C=-B+D. This condition will again establish a vertical null.Since signals A+B-(C+D) and A-+C(B+D) are processed through theirrespective circuitry completely independently of each other, verticaland horizontal repositioning can be accomplished simultaneously. As thetarget 12 moves to new positions the detector assembly 14 will tracksaid target 12 in response to vertical and horizontal error signals.

It is understood that when the source of light 12 falls elsewhere on thequadrant array detector 18, an entirely different signal amplituderelationship will exist between said outputs A, B, C, and D; however,the same summing and differencing techniques are used to accomplishrepositioning of the flexure means l6 whatever the relationship may be.

DESCRIPTION OF THE MODIFIED EMBODIMENT In the optical missile guidancesystem embodiment shown in FIG. 6, those parts which are identical tocorresponding parts of the preferred embodiment will be given the sameidentify ing numbers.

Suitably installed in a missile 200 is the optical missile guidancesystem, not shown, which includes all the elements associated with theoptical control device 10. All the elements of said control device 10perform the same function when used in said guidance system. The opticalmissile guidance system further includes a missile motion stabilizationmeans 204, a roll stabilization means 206, two vertical control fins 208and 210 and their respective closed-loop torquer motors 209 and 211mounted on said missile 200, and two horizontal control fins 212 and 214and their respective closed-loop torquer motors 213 and 2l5 mounted onsaid missile 200.

Missile motion stabilization is required to preclude lateral missilemotion errors from being sensed and corrected for by the flexure means16. The control fins 208, 210, 212, and 214, are responsive to saidmissile motion stabilization means 204 which will generally contain agyro to sense and provide corrective signal outputs for lateral missilemovements resulting from crosswinds, dense airmasses or the like.

The optical missile guidance system will also require rollstabilization. Too much roll could produce interaction between thechannels and eventually bring about instability of the system. Since allsystems have a finite response time, it is necessary for reliableoperation that during this response time the missile does not roll toomuch. The control fins 208, 2l0, 212, and 214 are responsive to saidroll stabilization means 206 to preclude system instability resultingfrom missile roll.

The missile motion stabilization means, the roll stabilization means andthe vertical and horizontal control fin means are of the conventionalvariety and are not shown in detail on the drawing.

Said missile 200 is guided to its target by means of vertical andhorizontal error signals derived in the optical control device [0available at terminals 216 and 218, respectively, shown in FIG. 1. Sincethe said error signals used to control the flexure means 16 representangular error between the boresight of the flexure means 16 as well asthe missile 200 and the target source oflight 12, these same signals areused to guide the missile to the target. FIG. 7 shows the relationshipof the quadrant array detector 18 to the control fins 208, 210, 212, and214. A vertical position error signal appearing at terminal 216 would bepassed to closed-loop torquer motors 209 and 21! for control of verticalcontrol fins 208 and 210, respectively. A horizontal position errorsignal appearing at terminal 218 would be passed to closed-loop torquermotors 213 and 215 for control of horizontal control fins 212 and 214,respectively.

The vertical control fins 208 and M although functioning independentlyof each other respond identically to the same vertical position errorsignal to control missile vertical position. The horizontal control fins112 and 214 although functioning independently of each other respondidentically to the same horizontal position error signal to controlmissile horizontal position.

It may be parenthetically mentioned that missile motion stabilizationand roll stabilization control signals may be independently superimposedupon the horizontal and vertical control signals being communicated totheir respective control fins.

MODE OF OPERATION OF MODIFIED EMBODIMENT To properly accomplish targetacquisition, the missile 200 must be suitably mounted on an aircraft andhave its optical missile guidance system directed along the line offlight of the aircraft. Further, the detector assembly 14, comprised ofthe two-axis electromagnetic flexure means l6 and the quadrant arraydetector means 18, must be boresighted with the pilot's optical gunsight.

The pilot of the aircraft will, where possible, visually acquire thetarget he desires to track. The pilot will then maneuver the aircraftuntil the optical gunsight is centered on the target. The pilot willthen throw switch 70 to the target tracking mode position.

One of several conventional techniques, such as a closedcircuittelevision monitor displaying to the pilot what the missile sees, or atarget correlation computer to verify the integrity of the targetsignal, may be used to verify missile-tracking system lock-on withrespect to the target.

At the instant the pilot is assured, by whatever electronic verificationsystem he is using, that proper target lock-on does exist, he willrelease missile 200 from the aircraft to approach the chosen target asdirected by its optical missile guidance system It]. It is noted,although not shown, that horizontal and vertical control signals cannotbe provided to the missile 200 control fins prior to release of missile200 from the aircrafi to avoid possible instabilities in control of theaircraft.

Once the missile 200 is launched from the aircraft, it is understoodthat guidance and control signals will be obtained and processed asdescribed in the preferred embodiment.

While the specific details have been herein shown and described, theinvention is not confined thereto, as other sub stitutions can be madewithin the spirit and scope of the invention.

It is claimed:

1. An optical control device comprising:

a quadrant array detector means responsive to a localized source oflight and having outputs A, B, C, and D, from quadrants 2, l, 3, and 4,respectively, each variable as a function of their respective exposureto said localized source of light;

an optical means intermediate said quadrant array detector means andsaid source of light for collecting said light to form an image on saidquadrant array detector means;

a flexure means for flexing along two axes in response to anelectromagnetic field, said flexure means having connected thereto saidquadrant array detector means for controlling the position of saiddetector means relative to said localized source of light so as toproportion said source of localized light equally in each of saiddetector quadrants;

a first means responsive to said quadrant array detector means forderiving reference signal A+B+C+D;

a second means responsive to said quadrant array detector means forderiving signal A+B-(C+D);

a third means responsive to said quadrant array detector means forderiving signal A+C(B+D);

a threshold detector means responsive to said first means as a functionof a predetermined signal-to-noise ratio to control the flow of signalsA+B-(C+D) and A+C(B+D) therethrough;

first and second amplifier means responsive, respectively, to

signals A-i-B-( C+D) and A+C( 8+0) for providing current representingtrue angular errors between said quadrant array detector means and aline of sight to said localized source of light;

said flexure means being responsive to said first and second amplifiermeans currents to reposition itself until said quadrant array detectoroutputs are equal;

said first amplifier means current controlling vertical position axis ofsaid flexure means; and

said second amplifier means current controlling horizontal position axisof said fiexure means.

2. An optical control device as claimed in claim 1, including a filtermeans intermediate said optical means and said localized light source tolimit spectral response of said quadrant array detector.

3. An optical control device as recited in claim 1, wherein the deviceis used as a closed-loop tracking system.

4. A closed-loop tracking system as recited in claim 3, including anoptical magnifying scope mounted externally on said tracking system foraccomplishing tracking system target lock-on by visual observance.

S. An optical control device as recited in claim 1, wherein the deviceis used as a guidance system further including roll and lateral missilemotion stabilization.

6. An optical control device are recited in claim I, wherein saidlocalized source of light approaches that of a point source and whosewavelength of emission lies in the visible or near infrared portions ofthe electromagnetic spectrum.

7. An optical control device as recited in claim 1, wherein saidquadrant array detector means comprises:

four photodiocles;

each of said diodes forming one quadrant and being suitably mounted in asingle package with close spacing of each diode relative to the others;

each diode having a signal output.

8. An optical control device as recited in claim 1, wherein said filtermeans is of predetermined transmission charac teristics as a function ofthe intended use of said optical control device.

9. An optical control device, as recited in claim I, wherein saidflexure means comprises:

a means for providing cantilevered support;

a first element responsive to current for bidirectionally positioningsaid cantilevered means in its vertical plane;

a second element responsive to current for bidirectionally positioningsaid cantilevered means in its horizontal plane;

said first and second elements being independently respon sivesimultaneously;

a first pickoff element magnetically responsive to said first element togenerate a current therein for use in a series flow closed-looprelationship with a first electronic control means which positions saidfirst element;

a second pickoff element magnetically responsive to said second elementto generate a current therein for use in a series flow closed-looprelationship with a second elec' tronic control means which positionssaid second element.

10. An optical control device as recited in claim 1, wherein said firstmeans responsive to said quadrant array detector means is a pulsetransformer having inputs A, B, C, and D, and an output A-l-B+C+D.

ll. An optical control device as recited in claim 1, wherein said secondmeans responsive to said quadrant array detector means comprises:

a first subtraction means having inputs A and D, and an output A-D;

a second subtraction means having inputs 8 and C. and an output B-C;

an addition means having inputs from said first and second subtractionmeans. and an output A+B( C-i-D).

12. An optical control device as recited in claim 1, wherein said thirdmeans responsive to said quadrant array detector means comprises:

a first subtraction means having inputs A and D, and an output 4-0;

a second subtraction means having inputs B and C, and an output 8-6;

a third subtraction means having inputs from said first and secondsubtraction means, and an output A+C( B+D). 13. An optical controldevice as recited in claim I, wherein said first and second amplifiermeans each comprise:

an input network to provide for pulse averaging and pulse stretching;

a pulse driver stage responsive to said input network for passing saidsignal to a holding circuit;

said holding circuit having an output upon a command signal from saidthreshold detector means;

a high-gain servoamplifier being responsive to said holding circuitoutput to generate an output control signal proportional to said signalinput.

14. A photosensitive electromagnetic detector means comprising:

a means for providing cantilevered support;

a first element responsive to current for bidirectionally positioningsaid cantilevered means in its vertical plane;

a second element responsive to current for bidirectionally positioningsaid cantilevered means in its horizontal plane;

said first and second elements being independently responsivesimultaneously;

a first pickoff element magnetically responsive to said first element togenerate a current therein for use in a series flow closed-looprelationship with a first electronic control means which positions saidfirst element;

a second pickofi' element magnetically responsive to said second elementto generate a current therein for use in a series flow closed-looprelationship with a second electronic control means which positions saidsecond element;

a quadrant array detector means rigidly mounted on the free end oi'saidcantilevered means;

said quadrant array detector means being comprised of four photodiodeswith each of said diodes forming one quadrant and being suitably mountedin a single package with close spacing of each diode relative to theothers to optimize the quadrant photosensitive area; and

said quadrant array detector means being responsive to a localizedsource of light and having outputs A, B, C, and D, from quadrants 2, l,3, and 4, respectively, each variable as a function of their respectiveexposure to said localized source of light.

15. A flexure means for flexing along two axes in response to anelectromagnetic field, said flexure means comprising:

a means for providing cantilevered support;

a first element responsive to current for bidirectionally positioningsaid cantilevered means in its vertical plane;

a second element responsive to current for bidirectionally positioningsaid cantilevered means in its horizontal plane;

a first pickofl' element magnetically responsive to said first elementto generate a current therein for use in a series flow closed-looprelationship with a first electronic control means which positions saidfirst element; and

a second pickoff element magnetically responsive to said second elementto generate a current therein for use in a series flow closed-looprelationship with a second electronic control means which position saidsecond element.

16. A tracking device comprising:

array detector means having at least three sections responsive to asource of light, each section having an output which represents itsexlposure to said source of light;

flexure means operative y connected to said array detector means forcontrolling the position of said array detector means relative to saidsource of light to proportion said source of light equally in eachsection;

first means responsive to said outputs of said array detector means forgenerating a first signal;

second means responsive to said outputs of said array detector means forgenerating a second signal;

third means responsive to said outputs of said array detector means forgenerating a reference signal; and

threshold detector means responsive to said reference signal to controlthe fiow of said first and second signals unless a predeterminedsignal-to-noise ratio has been exceeded;

said l'lexure means including a cantilevered shaft that bends inresponse to a magnetic field to reposition itself until said outputs ofsaid array detector means are equal, said first and second signalscontrolling vertical and horizontal bending, respectively, of saidflexure means.

17. The tracking device, as recited in claim 16, wherein said arraydetector means has four quadrants, each quadrant corresponding to one ofsaid sections, said first signal being generated when first opposinghalves of said quadrant sections are not exposed to the same amount ofsaid source of light, said second signal being generated when secondopposing halves of said quadrant sections which are perpendicular tosaid first opposing halves are not exposed to the same amount of saidsource of light.

18. The tracking device, as recited in claim 17, further comprisingamplifier means for magnifying said first and second signals to driveperpendicularly located coils on said flexure means to generate saidmagnetic fields.

19. The tracking device, as recited in claim 17, further comprising:

optical means intermediate said array detector means and said source oflight; and

pickup means for determining the position of said flexure means after arepositioning has taken place.

1. An optical control device comprising: a quadrant array detector meansresponsive to a localized source of light and having outputs A, B, C,and D, from quadrants 2, 1, 3, and 4, respectively, each variable as afunction of their respective exposure to said localized source of light;an optical means intermediate said quadrant array detector means andsaid source of light for collecting said light to form an image on saidquadrant array detector means; a flexure means for flexing along twoaxes in response to an electromagnetic field, said flexure means havingconnected thereto said quadrant array detector means for controlling theposition of said detector means relative to said localized source oflight so as to proportion said source of localized light equally in eachof said detector quadrants; a first means responsive to said quadrantarray detector means for deriving reference signal A+B+C+D; a secondmeans responsive to said quadrant array detector means for derivingsignal A+B-(C+D); a third means responsive to said quadrant arraydetector means for deriving signal A+C-(B+D); a threshold detector meansresponsive to said first means as a function of a predeterminedsignal-to-noise ratio to control the flow of signals A+B-(C+D) andA+C-(B+D) therethrough; first and second amplifier means responsive,respectively, to signals A+B-(C+D) and A+C-(B+D) for providing currentrepresenting true angular errors between said quadrant array detectormeans and a line of sight to said localized source of light; saidflexure means being responsive to said first and second amplifier meanscurrents to reposition itself until said quadrant array detector outputsare equal; said first amplifier means current controlling verticalposition axis of said flexure means; and said second amplifier meanscurrent controlling horizontal position axis of said flexure means. 2.An optical control device as claimed in claim 1, including a filtermeans intermediate said optical means and said localized light source tolimit spectral response of said quadrant array detector.
 3. An opticalcontrol device as recited in claim 1, wherein the devicE is used as aclosed-loop tracking system.
 4. A closed-loop tracking system as recitedin claim 3, including an optical magnifying scope mounted externally onsaid tracking system for accomplishing tracking system target lock-on byvisual observance.
 5. An optical control device as recited in claim 1,wherein the device is used as a guidance system further including rolland lateral missile motion stabilization.
 6. An optical control deviceare recited in claim 1, wherein said localized source of lightapproaches that of a point source and whose wavelength of emission liesin the visible or near infrared portions of the electromagneticspectrum.
 7. An optical control device as recited in claim 1, whereinsaid quadrant array detector means comprises: four photodiodes; each ofsaid diodes forming one quadrant and being suitably mounted in a singlepackage with close spacing of each diode relative to the others; eachdiode having a signal output.
 8. An optical control device as recited inclaim 1, wherein said filter means is of predetermined transmissioncharacteristics as a function of the intended use of said opticalcontrol device.
 9. An optical control device, as recited in claim 1,wherein said flexure means comprises: a means for providing cantileveredsupport; a first element responsive to current for bidirectionallypositioning said cantilevered means in its vertical plane; a secondelement responsive to current for bidirectionally positioning saidcantilevered means in its horizontal plane; said first and secondelements being independently responsive simultaneously; a first pickoffelement magnetically responsive to said first element to generate acurrent therein for use in a series flow closed-loop relationship with afirst electronic control means which positions said first element; asecond pickoff element magnetically responsive to said second element togenerate a current therein for use in a series flow closed-looprelationship with a second electronic control means which positions saidsecond element.
 10. An optical control device as recited in claim 1,wherein said first means responsive to said quadrant array detectormeans is a pulse transformer having inputs A, B, C, and D, and an outputA+B+C+D.
 11. An optical control device as recited in claim 1, whereinsaid second means responsive to said quadrant array detector meanscomprises: a first subtraction means having inputs A and D, and anoutput A-D; a second subtraction means having inputs B and C, and anoutput B-C; an addition means having inputs from said first and secondsubtraction means, and an output A+B-(C+D).
 12. An optical controldevice as recited in claim 1, wherein said third means responsive tosaid quadrant array detector means comprises: a first subtraction meanshaving inputs A and D, and an output A-D; a second subtraction meanshaving inputs B and C, and an output B-C; a third subtraction meanshaving inputs from said first and second subtraction means, and anoutput A+C-(B+D).
 13. An optical control device as recited in claim 1,wherein said first and second amplifier means each comprise: an inputnetwork to provide for pulse averaging and pulse stretching; a pulsedriver stage responsive to said input network for passing said signal toa holding circuit; said holding circuit having an output upon a commandsignal from said threshold detector means; a high-gain servoamplifierbeing responsive to said holding circuit output to generate an outputcontrol signal proportional to said signal input.
 14. A photosensitiveelectromagnetic detector means comprising: a means for providingcantilevered support; a first element responsive to current forbidirectionally positioning said cantilevered meanS in its verticalplane; a second element responsive to current for bidirectionallypositioning said cantilevered means in its horizontal plane; said firstand second elements being independently responsive simultaneously; afirst pickoff element magnetically responsive to said first element togenerate a current therein for use in a series flow closed-looprelationship with a first electronic control means which positions saidfirst element; a second pickoff element magnetically responsive to saidsecond element to generate a current therein for use in a series flowclosed-loop relationship with a second electronic control means whichpositions said second element; a quadrant array detector means rigidlymounted on the free end of said cantilevered means; said quadrant arraydetector means being comprised of four photodiodes with each of saiddiodes forming one quadrant and being suitably mounted in a singlepackage with close spacing of each diode relative to the others tooptimize the quadrant photosensitive area; and said quadrant arraydetector means being responsive to a localized source of light andhaving outputs A, B, C, and D, from quadrants 2, 1, 3, and 4,respectively, each variable as a function of their respective exposureto said localized source of light.
 15. A flexure means for flexing alongtwo axes in response to an electromagnetic field, said flexure meanscomprising: a means for providing cantilevered support; a first elementresponsive to current for bidirectionally positioning said cantileveredmeans in its vertical plane; a second element responsive to current forbidirectionally positioning said cantilevered means in its horizontalplane; a first pickoff element magnetically responsive to said firstelement to generate a current therein for use in a series flowclosed-loop relationship with a first electronic control means whichpositions said first element; and a second pickoff element magneticallyresponsive to said second element to generate a current therein for usein a series flow closed-loop relationship with a second electroniccontrol means which position said second element.
 16. A tracking devicecomprising: array detector means having at least three sectionsresponsive to a source of light, each section having an output whichrepresents its exposure to said source of light; flexure meansoperatively connected to said array detector means for controlling theposition of said array detector means relative to said source of lightto proportion said source of light equally in each section; first meansresponsive to said outputs of said array detector means for generating afirst signal; second means responsive to said outputs of said arraydetector means for generating a second signal; third means responsive tosaid outputs of said array detector means for generating a referencesignal; and threshold detector means responsive to said reference signalto control the flow of said first and second signals unless apredetermined signal-to-noise ratio has been exceeded; said flexuremeans including a cantilevered shaft that bends in response to amagnetic field to reposition itself until said outputs of said arraydetector means are equal, said first and second signals controllingvertical and horizontal bending, respectively, of said flexure means.17. The tracking device, as recited in claim 16, wherein said arraydetector means has four quadrants, each quadrant corresponding to one ofsaid sections, said first signal being generated when first opposinghalves of said quadrant sections are not exposed to the same amount ofsaid source of light, said second signal being generated when secondopposing halves of said quadrant sections which are perpendicular tosaid first opposing halves are not exposed to the same amount of saidsource of light.
 18. The tracking device, as recited in claim 17,further comprising amplifier means for maGnifying said first and secondsignals to drive perpendicularly located coils on said flexure means togenerate said magnetic fields.
 19. The tracking device, as recited inclaim 17, further comprising: optical means intermediate said arraydetector means and said source of light; and pickup means fordetermining the position of said flexure means after a repositioning hastaken place.